This invention relates to lubricant formulations containing mixtures of i) the reaction product of at least one C5-C60 carboxylic acid and at least one amine selected from the group consisting of guanidine, aminoguanidine, urea, thioruea and salts thereof and ii) phosphorus-containing dispersants. The lubricant formulations of the present invention exhibit excellent low and high temperature rheology and are particularly suited for use in automotive and industrial gear applications. Lubricants of the present invention exhibit improved performance properties, such as increased axle efficiencies and lower axle temperatures, compared to lubricant formulations that do not contain said mixtures.
The primary function of a gear lubricant is to provide a high degree of reliability and durability in the service life of gear equipment. Gear lubricants may also contribute to improving the fuel economy of vehicles by improving the axle efficiency. See, for example, O""Connor et al., The Relationship Between Laboratory Axle Efficiency and Vehicle Fuel Consumption (SAE Paper No. 811206).
In the paper by O""Connor et al., entitled Axle Efficiencyxe2x80x94Response to Synthetic Lubricant Components (SAE Paper No. 821181), the authors state that xe2x80x9c[i]nvestigations with both partial- and full-synthetic base formulations have shown improvements compared to conventional petroleum base gear oils. Maximum benefits are gained with total synthetic base type formulations.xe2x80x9d
Limited slip differentials are designed to restrict differentiation in a vehicle operating on a slippery surface. The limited slip characteristic is obtained by modifying a standard differential with the addition of a clutch. This clutch has the property of forcing both axle shafts to turn with the ring gear when the vehicle operates on a slippery surface. Limited slip differentials contain a slow-moving clutch. At low sliding velocities this clutch is prone to stick and then slip in a repetitive fashion unless a lubricant with the proper frictional characteristics is used. This stick-slip effect is very objectionable as it can result in loud chatter noises and severe vibration. The paper by John W. Allen, entitled Lubricants for Limited Slip Differentials (SAE Paper No. 660779), provides some background on the problems associated with limited slip differentials and some proposed lubricant solutions. The Allen paper does not teach or suggest the additives of the present invention or their use in lubricant formulations.
Power dividers are the linkages in the drivetrain that direct engine torque to gripping wheels rather than slipping wheels. The power divider""s application is similar to the limited slip clutches in light duty axles. There are many types of power dividers, their overall purpose is to transmit torque to both sets of wheels or between the front and rear axles. In one particular design, this is accomplished by using a set of wedges between two cylindrical cams whose mating surfaces with the wedges are lobed. These lock for transmittal but slide to avoid torque buildup. When too much torque has built up without sliding, the wedges break the momentary welds formed. This is accompanied by a loud snap that can propel the truck sideways. Malfunctioning power dividers can result in broken axles.
Hutchison et al., in U.S. Pat. No. 4,948,523, discloses a lubricating composition that contains a silver protective agent. The silver protective agent comprises the reaction product of a C5-C60 carboxylic acid and at least one amine selected from the group consisting of: 1) guanidine, urea and thioruea compounds; 2) C1-C20 hydrocarbyl or hydroxy-substituted hydrocarbyl mono-amines, alkylene diamines; and 3) polyalkylene polyamines and N-alkyl glycine. This patent is directed to lubricating oil additives for medium speed diesel engines, such as locomotive engines, which have silver parts in the engine. Large, medium-speed diesel engines often contain silver protected components, such as bearings, and, as such, the lubricating oils may not contain the typical zinc containing wear inhibitors which attack the silver coated parts. This patent does not teach the use of the reaction products of the present invention in gear oil formulations or the improvements in, for example, axle efficiency, limited slip performance or power divider performance exhibited by the compositions of the present invention.
The present invention is directed to a lubricant composition comprising:
(A) an oil of lubricating viscosity;
(B) the reaction product of at least one C5-C60 carboxylic acid and at least one amine selected from the group consisting of guanidine, aminoguanidine, urea, thioruea and salts thereof;
(C) a phosphorus-containing dispersant; and
(D) a gear additive package.
The lubricant formulations of the present invention exhibit excellent low and high temperature rheology and are particularly suited for use in automotive and industrial gear applications. The lubricant formulations of the present invention exhibit improved performance properties such as increased axle efficiencies and lower axle temperatures compared to lubricant formulations that do not contain said reaction products. Further, the present invention is directed to the use of mixtures of the reaction product (B) and the phosphorus-containing dispersant (C) for increasing axle efficiencies and lowering axle temperatures in automotive and industrial gear applications.